Microcell Structure Research Articles

Reliability Optimization in the Design and Implementation of 6G Vehicle-to-Infrastructure Systems for Emergency Management in a Smart City Environment

Building on the microcell structure that utilizes carrier frequencies substantially above current 5G cellular networks can pose significant challenges to future generation cellular communication. In particular, the operational reliability of communication systems that support mission-critical services can be greatly affected by variations in vehicle velocity, rain-induced attenuation, and depolarization. The mandatory inclusion of eCall emergency systems in motor vehicles sold across the European Union since 2018 puts tremendous challenges to 6G development in emergency management given the fact that many road accidents occur under heavy rainfall. Addressing the urgent needs of reliability assessment of 6G-based emergency management systems within a smart city, this article takes an in-depth look at technical issues concerning the design and implementation aspects of the underlying vehicle-to-infrastructure (V2I) communication systems for optimizing reliability in a smart city environment is studied under the co-existence of both 5G and 6G network backbones.

A Novel Semi-Distributed OFDMA for Indoor Visible Light Communications

In this paper, a novel OFDMA architecture based on the characteristics of the indoor visible light communication network is introduced. It is characterized by a microcell structure and frequent terminal switching. The OFDM proposed in this paper adopts DCO-OFDM modulation technology, which is determined by the consideration of the nonlinear and non-negative signal transmission characteristics of LEDs, and the SLM algorithm is also introduced to reduce PAPR. The simulation results demonstrate that the SLM algorithm can effectively reduce the PAPR of DCO-OFDM, which increases the probability that the signal in the entire system is lower than the PAPR threshold. Compared with the SLM algorithm, its CDF probability is increased by about 40%, and the SNR is also improved by 2.5 dB. The proposed OFDMA is a semi-distributed structure that is controlled by the DME to allocate subcarriers to each AP, and each has the ability to allocate subcarriers independently. Based on this architecture, an idea of dynamic subcarrier allocation is proposed, and uses the optical power received by the terminal as the SIR index to allocate different subcarriers to different SIR terminals and optimize the utilization of resources. The results of the modeling and simulation indicate that when the subcarrier allocation algorithm and method of reducing PAPR via SLM are combined, the BER of the system is significantly improved; when the SNR is 13 dB, the BER can be reduced to less than 10-6. This method can help the system reach the perfect communication target with a lower SNR, allowing the system to achieve better BER performance with less power consumption.

Superhydrophobicity on hierarchical periodic surface structures fabricated via direct laser writing and direct laser interference patterning on an aluminium alloy

Multi-scaled hierarchical surface microstructures are fabricated on Al2024 alloy using Direct Laser Writing and Direct Laser Interference Patterning. During the manufacturing procedure two distinct laser sources are used, including an ultra-violet nanosecond laser system that produces microcell structures with different dimensions through Direct Laser Writing. Posteriorly, an infrared picosecond laser source is used to fabricate sub-micron features on the previously patterned microcells. Thus, the fabricated multi-scaled hierarchical structures are a closer representation of what is observed in nature. Water contact angle measurements are carried out in order to assess the wettability response, which revealed superhydrophobicity one week posterior to the fabrication, with measured contact angles up to 161.5 ± 3°.

Characterization of 1.2×1.2 mm2 silicon photomultipliers with Ce:LYSO, Ce:GAGG, and Pr:LuAG scintillation crystals as detector modules for positron emission tomography

The design of a positron emission tomography (PET) scanner is specially challenging since it should not compromise high spatial resolution, high sensitivity, high count-rate capability, and good energy and time resolution. The geometrical design of the system alongside the characteristics of the individual PET detector modules contributes to the overall performance of the scanner. The detector performance is mainly influenced by the characteristics of the photo-detector and the scintillation crystal. Although silicon photomultipliers (SiPMs) have already proven to be promising photo-detectors for PET, their performance is highly influenced by micro-cell structure and production technology. Therefore, five types of SiPMs produced by KETEK with an active area size of 1.2 × 1.2 mm2 were characterized in this study. The SiPMs differed in the production technology and had micro-cell sizes of 25, 50, 75, and 100 μm. Performance of the SiPMs was evaluated in terms of their breakdown voltage, temperature sensitivity, dark count rate, and correlated noise probability. Subsequently, energy resolution and coincidence time resolution (CTR) of the SiPMs were measured with five types of crystals, including two Ce:LYSO, two Ce:GAGG, and one Pr:LuAG. Two crystals with a geometry of 1.5 × 1.5 × 6 mm3 were available from each type. The best CTR achieved was ∼ 240 ps, which was obtained with the Ce:LYSO crystals coupled to the 50 μm SiPM produced with the trench technology. The best energy resolution for the 511 keV photo-peak was ∼ 11% and was obtained with the same SiPM coupled to the Ce:GAGG crystals.

G0300305 アルミナスラリーの一方向凍結を利用したアルミナ柱状構造の制御と機械的性質

The micro-columnar-structure in alumina was controlled by the process which consist of unidirectional solidification, freeze-drying and sintering of alumina-slurry. In particular, the effect of additives in the alumina slurry on the formation of columnar-structure was investigated. In the sample made from the slurry containing sodium chloride, the direction of columnar-structure of alumina was randomly arranged, while the columnar-structure was unidirectionally arranged in the sample obtained from the slurry without additives. On the other hand, the alumina sample obtained from the slurry containing ethylene glycol shows the micro-cell structure. The mechanical property in micro-columnar-structured alumina / unsaturated polyester composites was strongly depended on the width and spacing of columnar-structured alumina.

A comparative study between felted and triaxial compressed polymer foams on cushion performance

A widely used industrial felted foam was compared to a volumetrically heated and compressed foam in this study in terms of cushion performance. The off-the-shelf melamine open cell foam and polyurethane open cell foam were triaxially heated and compressed via an in-house-made device, and energy dissipation was then compared to the felted off-the-shelf open cell melamine and the polyurethane foam. The hysteresis cycle compression test and impact test, in conjunction with a high-speed video camera, were conducted to measure the energy dissipation, G-value, and the Poisson’s ratio. Scanning electron microscopy was used to investigate the cellular morphology before and after the felting and volumetric heat and compression. The study showed that both felted foam and triaxial compressed foam demonstrated reasonably well the cushion performance due to the presence of auxetic and microcell structures.

Optimum Design of Quenching Capacitor Integrated Silicon Photomultipliers for TOF-PET Application

The prototype SiPM was designed and fabricated for MRI compatible PET using the customized CMOS process at National Nanofab Center in KAIST. The SiPM was designed to have a size of 3x3 mm2 composed of micro-cells of 65x65 μm2 with a fill factor of 68%. The size of a micro-cell was determined by optimization between the photon detection efficiency (PDE) and the dynamic range for the photons of 511 keV from LYSO crystal. In the micro-cell structure, a specially designed quenching capacitor (QC) is added parallel to quenching resistor using the Metal-Insulator-Metal (MIM) process. This QC integrated SiPMs (QC-SiPM) was devised to realize rapid response of output pulses and to enhance the timing resolution of SiPM. Coincidence timing resolution of PET detectors depends on the output pulse shapes which are the convolution of the intrinsic pulse shape of scintillation crystals and the single photon pulse shape at the micro-cell in a SiPM. A quenching capacitor parallel to a quenching resistor provides a fast current path at the beginning stage of avalanche process, than reduces rising time of single photon pulse shape. In this study the rise time of the QC-SiPM signal was analyzed to be 22.5 ns while that for the regular SiPM was 34.3 ns.

A bulk metal/ceramic composite material with a cellular structure

A bulk metal/ceramic composite material with a honeycomb-like micro-cell structure has been prepared by sintering the spherical Al90Mn9Ce1 alloy powders clad by Al2O3 nano-powder with the spark plasma sintering (SPS) technique. The as-prepared material consists of Al90Mn9Ce1 alloy cell and closed Al2O3 ceramic cell wall. The diameter of the cells is about 20–40 μm, while a thickness of the cell wall is about 1–2 μm. The ultimate compressive strength of the as-sintered materials is about 514 MPa, while its fracture strain is up to about 0.65 %. This composite material might possess good anti-corrosion, thermal endurance and other potential properties due to its unique microstructure. The result shows that the Al90Mn9Ce1/Al2O3 composite powders can be sintered by spark plasma sintering technique despite the large difference in their sintering temperature. This work offers a way of designing and preparing metal/ceramic composite material with functional property.

Microstructures and nanostructures of high Andean Penaincisalia lycaenid butterfly scales (Lepidoptera: Lycaenidae): descriptions and interpretations

The scales of one high Andean eumaeine lycaenid butterfly species with pale dorsal coloration and four species with vivid dorsal colour were investigated using field emission scanning electron microscopy. The micro‐ and nanostructures are illustrated, described, measured, and interpreted. The vivid colours in the species are caused by a pepper‐pot nanostructure of Urania‐type scales. This nanostructure is a three‐dimensional lattice within the body of the individual scale. The scales of the non‐vivid orange species are lacking this nanostructure and the surfaces of their scales show high microstructure irregularities. This absence of vivid colour may be correlated with thermal regulation. The irregularity of the scale microstructures suggests a heavy environmental pressure on the populations sampled. Previously unknown structural variations of Urania‐type scales are also described. The existence of closed scale microcell structures, explained as an apomorphic character in the tribe Eumaeini, most probably evolved independently several times. It is hypothesized that scale micro‐ and nanostructure modifications develop syntopically within a population, which in turn can lead to rapid diversification.

54.1: Flexible Electrophoretic Displays with Jet-Printed Active-Matrix Backplanes

We report on the integration of electrophoretic media with flexible backplanes. The active-matrix backplanes are based on amorphous-silicon or on organic-semiconductor technology. Conventional photolithography was fully replaced by jet-printing. Flexible electrophoretic media is fabricated by photolithography and by molding of micro-cell structures. Various aspects will be addressed, concerning the media, the backplanes and the integration.

Crystallization Behavior of Polyamide-6 Microcellular Nanocomposites

The crystallization behaviors of polyamide-6 (PA-6) and its nanocomposites undergoing the microcellular injection molding process are studied using Transmission Electron Microscopy (TEM), X-ray Diffractometer (XRD), Polarized Optical Microscopy (POM), and Differential Scanning Calorimetry (DSC). The relationships among the morphology, the mechanical property of the molded parts, and the crystallization behavior are investigated. With the addition of nanoclays in microcellular injection molded parts, the growth of the γ-form crystal is suppressed and the formation of γ-form crystals is promoted. Both nanoclay and dissolved gas have a big influence on PA-6 crystalline structures. The existence of nanoclay increases the initial crystallization rate. But with extra addition of nanoclays in the polymer matrix, the increase of crystallization rate is reduced. Microcellular injection molded nanocomposites with proper amount of nanoclays possess the maximum crystallization activation energy and produce a finer and denser microcell structure which leads to better mechanical properties.

무선 네트워크에서 사용자 이동 패턴을 사용한 이동성 예측 기법

무선 셀룰러 환경에서 가장 중요한 기술중의 하나가 사용자의 이동성(Mobility)을 보장하기 위한 핸드오프 기술이다 이러한 핸드오프 기술은 사용자가 이동할 주변 셀에 대한 대역폭 예약과 관련이 있다. 무선 셀룰러 환경에서 효과적인 대역폭 사용을 위하여. 사용자의 이동성을 예즉하는 기술은 핸드오프 호의 실패율(Dropping Probability)과 핸드오프 지연을 줄이는 효과적인 방법이다. 기존의 연구에서는 사무실, 빌딩과 같은 제한된 범위나 셀 간의 히스토리에 기반하여 이동 예측 알고리즘을 수행하였다. 그러나, 마이크로-셀(Micro-Cell) 구조나 도로가 복잡하게 구성되어 있는 도심에는 잘 적용되지 못한다는 단점이 있다. 이러한 단점을 극복하기 위하여, 본 논문에서는 낀 내부 이동 패턴을 저장한 히스토리를 이용하여, 사용자가 이동할 셀을 예측하는 새로운 알고리즘을 제안한다 Handoff if the most Important feature for the user's mobility in a cellular communication system, which is related to resource reservation at nearby cells. For efficient resource reservation, mobility prediction has been reported as an effective means to decrease call dropping probability and to shorten handoff latency in wireless cellular environments. Several early proposed handoff schemes making use of tile user's movement history on a cell-by-cell basis work on the assumption that the user's movements are restricted to the indoor locations such as an office or a building. However, those algorithms cannot be applied to a micro-cell structure or a metropolis with complicated structure of roads. In this paper, to overcome those drawbacks we propose a new mobility prediction algorithm, which stores and uses the history of the user's positions within the current cell to predict the next cell.

Fabrication of high-aspect-ratio sub-diffraction-limit microstructures by two-photon-absorption photopolymerization

Micro-cell structures with side-walls as thin as 0.70 μm and aspect ratios as high as 6.7 are fabricated by single-layer writing through two-photon-absorption (TPA) photopolymerization. The use of a moderate-numerical-aperture (N.A.) objective lens to obtain a much more elongated voxel and an in situ ultraviolet (UV) pre-exposure step to improve the sensitivity of TPA photopolymerization are the main factors responsible for the high aspect ratio and sub-diffraction-limit resolution that are achieved.

Performance study for a microcell hot spot embedded in CDMA macrocell systems

The code-division multiple-access (CDMA) system can provide more capacity than other systems, and the hierarchical layer of cells is required for system design. However, the problem is whether the same radio frequency (RF) channels used in a CDMA overlayed/underlayed macrocell and microcell structure also obtain a high capacity as in the homogeneous structure. We investigate the interference of uplink and downlink from both the microcell and macrocell under a hierarchical structure. A downlink power control scheme and two power control methods for the uplink are also considered. Performance measures such as blocking probability, C/I, capacity, and service hole area are also obtained by computer simulation. Besides, some extra efforts for a microcell are also noted, such as more power need to be transmitted by a microcell base station (BS) if the same RF channels are used in the hierarchical structure. The capacities of macrocell and microcell in the overlaying/underlaying structure are limited by the uplink and downlink, respectively. With downlink power control, the microcellular capacity can be increased. However, the combination of downlink power control for the microcell and C/I uplink power control for the macrocell causes the overall system capacity to significantly increase.

移動通信におけるマルチパスフェージングを補償する多重受信最ゆう復号法

A digital combining method with maximum liklihood error correction is proposed for improvement of multi-path fading. In personal communication systems, the quality of signal is maintained under the micro-cell structure which is about 200m. The proposed method is performed the ideal combining diversity by error correction of received signals at several base stations. In this paper, the principle of digital combining method is explained. The performance of this method is taken by computer simulation. Moreover, the prototype digital combining system for the personal communication is shown.